Was the old filter plugged up dirty?
I personally don't buy the K&N = better fuel efficiency idea.
If you look through their web site, you will not find ONE single corporate claim that their filters improve fuel economy over a clean, OEM filter. Why? Because if they did that, they'd have to prove it in court when they are sued by the EPA for misleading advertising. You better believe if they really thought their filters helped MPG, they'd be advertising the heck out of that.
Instead K&N relies on customer testimonials about MPG. Unfortunately, that anectdotal testimony isn't worth the electrons it travels on.